Some of the early SC actually had a tubular manifold as standard, suspect it was got at by the bean counters. TC is cast iron standard one,
You will need a different camshaft, but not as easy as just fitting a Mk3 / TC one, as they run in bearings, which your block doesn't have.
Also compression is up a bit.
Triumph also fitted the TC with a servo, I drove a TC with the servo removed many years ago, brakes weren't great.